//  solution_exercise_4_13.iml  2004-11-25

//  reverse_in_memory.iml  (c) 1997 - 2000 Kari Laitinen

//  The following program reads text from the keyboard. After the
//  space key has been pressed, the program displays the characters
//  of the entered text in reverse order. Thus if the user typed in
//
//      Hello 
//
//  the computer would respond
//
//      olleH
//

beginning_of_program:
      load_register_a_with_value       0
      set_memory_pointer               memory_for_characters
      store_register_a_to_memory

read_character:
      increment_memory_pointer
      call_subroutine                  read_and_echo_a_character
      store_register_a_to_memory
      load_register_b_with_value       ' '   // code for space
      jump_if_registers_equal          print_characters
      jump_to_address                  read_character

print_characters:
      output_byte_from_register_a
      decrement_memory_pointer
      load_register_a_from_memory
      jump_if_register_a_zero          all_characters_printed
      jump_to_address                  print_characters

all_characters_printed:
      stop_processing

//  The following subroutine is new this program.

read_and_echo_a_character:
      jump_if_input_not_ready          read_and_echo_a_character
      input_byte_to_register_a
      output_byte_from_register_a
      return_to_calling_program

memory_for_characters:     DATA        20